In sheet-processing presses, more particularly multicolor rotary presses, print quality depends to a considerable extent upon the ability of the consecutive gripper systems to retain the sheet reliably -- i.e., to prevent slipping and to retain the original register position as the sheet passes through the press. The use of coated papers and viscous inks makes heavy demands on the gripper facilities for ensuring proper register. One possibility is to increase the static friction by devising the retaining surfaces of the gripper facilities for positive engagement and another possibility is to increase the retaining forces by increasing the pressure between the retaining surfaces -- i.e., by increasing the pressure of the non-positive engagement.
DE-OS 2,421,346 discloses a gripper finger having a profiled retaining surface with fluting which extends parallel to the sheet front edge. A disadvantage is that when materials which produce considerable dust are being processed, the fluting greatly hinders the removal of the paper dust and other debris. Even the slightest accumulation thereof impairs the coefficient of friction and the static friction between the retaining surface of the finger and that retaining surface of the support for the gripper which cooperates with the gripper finger. Also, the grinding effect of the paper and the impacting against the support for the gripper cause rapid wear of the bead like protuberances of the finger, so that the positive engagement and static friction decrease.